1. Field of the Invention
The invention relates to a clutch device having a flywheel. More specifically, the present invention relates to a clutch device, in which the flywheel has a friction surface to facilitate clutch coupling to a frictional coupling portion of a clutch disk assembly. The present invention also relates to a frictional resistance generating mechanism generating a hysteresis torque for damping torsional vibrations.
2. Background Information
Conventionally, a flywheel is attached to a crankshaft of an engine for absorbing vibrations caused by variations in engine combustion. Further, a clutch device is arranged on a transmission side (i.e., in a position axially shifted toward the transmission) with respect to the flywheel. The clutch device usually includes a clutch disk assembly coupled to an input shaft of the transmission and a clutch cover assembly for biasing the frictional coupling portion of the clutch disk assembly toward the flywheel. The clutch disk assembly typically has a damper mechanism for absorbing and damping torsional vibrations. The damper mechanism has elastic members such as coil springs arranged for compression in a rotating direction.
A structure is also known in which the damper mechanism is not arranged in the clutch disk assembly, and rather is arranged between the flywheel and the crankshaft. In this structure, the flywheel is located on the output side of a vibrating system, in which the coil springs form a border between the output and input sides, so that an inertia on the output side is larger than that in other prior art. Consequently, the resonance rotation speed can be lower than an idling rotation speed so that damping performance is improved. The structure, in which the flywheel and the damper mechanism are combined as described above, provides a flywheel assembly and/or a flywheel damper.
When the flywheel assembly described above is supplied with torque variations from the engine, the springs in the damper mechanism are compressed in the rotating direction so that the torque vibrations are absorbed and damped. A power transmission system of a vehicle causes unwanted noises and vibrations such as gear collision noises of a drive system and muffled noises during driving. For reducing such noises and vibrations, it is necessary to lower torsional rigidity in an acceleration/deceleration torque range so that a torsional resonance frequency of the drive system may be lower than a service speed range of the engine. To lower the torsional rigidity in the damper mechanism, a torsion angle of an elastic member may be increased and/or a plurality of elastic members may be arranged to operate in series.
As the rigidity of the elastic member is lowered, such a situation may occur in which a rotation speed in a low speed range, e.g., lower than 500 rpm passes through a resonance point when starting or stopping the engine. This may cause excessively large torque vibrations that can result in the breaking of the damper mechanism. Alternatively, large noises and vibrations may occur. For overcoming the above problems, a lock mechanism has been used such that members on the opposite sides of the damper mechanism are locked together in a low speed range, and are released from each other to enable the operation of the damper mechanism in a high-speed range. This lock mechanism is generally formed of a lock member and an elastic member. The lock member is biased by the elastic member toward a locking position for preventing rotation of a member on the output side of the damper mechanism with respect to a member on the crankshaft side, and is moved by a centrifugal force to a releasing position for releasing the locked state. However, this lock mechanism complicates the structure, and increases the number of parts.
Additionally, when the flywheel assembly described above is supplied with torque variations from the engine, as mentioned, the springs in the damper mechanism are compressed in the rotating direction so that the torque variations are absorbed and damped. The damper mechanism has a frictional resistance generating mechanism formed of a plurality of members, and sliding occurs in the frictional resistance generating mechanism to generate a predetermined hysteresis torque when the springs are compressed. Thereby, the torsional vibrations are rapidly damped.
However, the frictional resistance generating mechanism is formed of a plurality of plates and friction members, and also has members supporting axially opposite sides of these members. Accordingly, the frictional resistance generating mechanism also requires many parts and a complicated structure as a whole.
Vibrations of vehicles include idling noises or rattling noises, driving noises or acceleration and deceleration rattling noises and muffled noises and tip-in/tip-out or low frequency vibrations.
The idling noises are rattling noises, which are generated from a transmission when a clutch pedal is released after shifting a gear position to neutral, e.g., during a stop at a traffic light. These noises are due to the fact that engine torque is low and varies to a large extent in response to engine combustion when an engine speed is in or near an idling range. In the idling range, tooth collisions occur between an input gear and a counter gear of the transmission.
The tip-in/tip-out or low frequency vibrations or large longitudinal vibrations of a vehicle body, which occurs when a driver rapidly depresses or releases a gas pedal. If a power transmission system has a low rigidity, the torque transmitted to the tires is reversibly transmitted from the tires to the power transmission system. Thus, this reaction causes excessive torque to be applied to the tires so that large longitudinal vibrations transitionally occur to vibrate the vehicle body longitudinally to a large extent.
The idling noises are significantly affected by torsion characteristics of a damper mechanism at and around a zero torque, and can be effectively prevented by reducing torsional rigidity at the zero torque. Conversely, for reducing the longitudinal vibrations of the tip-in/tip-out, torsion characteristics of the damper mechanism must be solid.
For overcoming the above problems, a damper mechanism has been provided such that uses two kinds of spring members for providing characteristics having two stages are used. In this mechanism, the torsional rigidity and a hysteresis torque are kept low in the first stage (low torsion angle region) of the torsion characteristics. This is effective in preventing noises during idling. Since the torsional rigidity and the hysteresis torque are kept high in the second stage (high torsion angle range) of the torsion characteristics, the longitudinal vibrations of tip-in/tip-out can be sufficiently damped.
Further, a damper mechanism has been known that can effectively absorb minute torsional vibrations by not operating a frictional resistance generating mechanism when the minute torsional vibrations are applied, e.g., due to combustion variations of the engine in the second stage of the torsion characteristics.
In the structure for deactivating the frictional resistance generating mechanism in response to minute vibrations, it is necessary to ensure a predetermined angular gap in the rotating direction between a spring member of a high rigidity in a compressed state, and the frictional resistance generating mechanism. The angle of this gap in the rotating direction takes an extremely small value, e.g., from about 0.2° to about 1.0°. This angular gap is maintained, e.g., between a pin and an edge of an aperture or a recess formed in a plate for passing the pin therethrough. This complicates a structure, and requires a difficult assembly operation for ensuring the angular space.
Moreover, a conventional damper mechanism is formed of an input member on the crankshaft side, an output member on the flywheel side, and a plurality of elastic members. The members on the input and output sides are plate members, and are provided with windows for accommodating the elastic members. The window is an aperture axially penetrating the member, and is configured to transmit a torque by supporting the circumferential ends in the rotating direction of the elastic member, and to support radially opposite ends and axially opposite sides of the elastic member.
However, various members of the damper mechanism have windows, which connect the spaces on the axially opposite sides to each other. Therefore, these windows are prone to transmit vibrational noises as well as sliding noises and others of the elastic members from the engine side to the transmission side.
In view of the above, there exists a need for clutch device that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.